1. Field of the Invention
The present invention relates to a zoom lens barrel that houses a plurality of lens frames holding a plurality of movable lens units and supporting the plurality of movable lens units so that the movable lens units are movable forward and rearward along an optical axis, an interchangeable lens including the zoom lens barrel, and a television camera device including the zoom lens barrel.
2. Description of the Related Art
In the related art, a television camera device, which takes a video or a motion picture, is provided with a lens barrel in which a focal length can be changed and the lens barrel includes a plurality of optical systems that include focus lens groups and zoom lens groups and a plurality of support frames that support the optical systems. Since the support frames are supported so as to be movable forward and rearward along an optical axis, a change in the focal length, that is, zooming can be performed when the support frames are mechanically driven in the direction of the optical axis.
In recent years, in regard to a video or a motion picture, a video having high resolution (a large number of pixels), for example, a ultra high-definition video like Super Hi-Vision (SHV) referred to as a 8K system or a high-definition video like a digital cinema referred to as a 4K system has spread rapidly. Since a video of the 8K system or the 4K system has the number of pixels 4 to 16 times the number of pixels of a Hi-vision (HV) video in the related art, a television lens used for a television camera device, which is used to take the video of the 8K system or the 4K system, requires high accuracy of aberration. Since focusing associated with zooming is needed to obtain high accuracy of aberration, the zoom lens groups need to be corrected according to a subject distance. Further, high-speed focusing is required to follow zooming in a manual mode.
Accordingly, JP2010-224526A discloses a lens barrel including an electromagnetic actuator used to drive a focus lens relative to a lens group unit in the direction of an optical axis so that a subject distance is kept substantially constant when the lens group unit including the focus lens is mechanically driven in the direction of the optical axis. A linear motor, which includes a coil for allowing current to flow and two magnets disposed so as to face each other with the coil interposed therebetween and forming a magnetic field around the coil, is used as the electromagnetic actuator.
Further, as a lens barrel that uses a linear motor as a drive mechanism for moving a barrel forward and rearward along an optical axis, JP2006-343470A discloses a lens barrel in which a stationary barrel is provided with a stationary-side coil, a second movable barrel is provided with a movable-side coil, a first movable barrel is provided with a magnet, the first movable barrel and the magnet are moved forward and rearward along an optical axis by the stationary-side coil, and the second movable barrel is moved along the optical axis by the movable-side coil. Accordingly, since the dimension of the magnet in the direction of the optical axis can be reduced, the dimension of the barrel in a collapsed state in the direction of the optical axis can be reduced.
Furthermore, JP2005-49729A discloses a lens barrel in which a magnet is provided on the outer periphery of a holding frame for a movable lens and a coil corresponding to the magnet is provided on the inner periphery of a barrel as a stationary side. Accordingly, a small VCM (voice coil motor) is formed in the barrel without being limited by a wire since a wire does not need to be led from a movable side.